1. Field of the Invention
The invention relates to a water-based latex of an acrylic modified waterborne alkyd or uralkyd dispersion in water. The invention also relates to a water-based latex based on non-waterborne or solvent-borne alkyds or uralkyds. Such hybrid resins are useful in a variety of coating compositions.
2. Description of Related Art
In recent years, considerable effort has been expended by the coatings industry to develop low or zero VOC containing coating formulations. Regulations to limit the amount of VOC content of industrial coatings have encouraged research and development to explore new technologies directed at reducing solvent emissions from industrial solvent-based coatings operations such as automotive, appliance, general metal, furniture, and the like. One technology involves the replacement of organic solvents with water and is of particular interest for the obvious reasons of availability, cost, and environmental acceptability. However, while the move from organic solvent-based compositions to aqueous compositions brings health and safety benefits, aqueous coating compositions must meet or exceed the performance standards expected from solvent-based compositions. The need to meet or exceed such performance standards places a premium on the characteristics and properties of waterborne polymer dispersions used in aqueous coating compositions.
Waterborne polymer dispersions have been prepared from each of the three primary industrial film-forming polymer types: polyesters, acrylics, and alkyds. Of the three polymer types, waterborne alkyd resins exhibit significantly higher storage stability and coating stability than the waterborne polyester or acrylic resins. In addition, waterborne alkyd resins, due to their low molecular weight, exhibit exceptional film forming ability which translates into very high gloss in the final coating film. Resistance properties are developed, as with traditional solvent-borne alkyds, via autooxidative crosslinking of the alkyd film. However, while waterbome alkyd polymers have shown, and continue to show promise, they have relatively slow "dry" and/or cure times, particularly at ambient temperatures. In an attempt to address such concerns, hybrids of waterborne alkyds and relatively high molecular weight acrylic polymers have received considerable attention and have demonstrated, in some cases, slight advantages over waterborne alkyd systems alone.
U.S. Pat. No. 4,413,073 describes the preparation of an aqueous dispersion of particles of a film-forming polymer comprising a pre-formed polymer and at least one polymer formed in situ ("multi-polymer particles"). The dispersion is prepared in the presence of an amphipathic stabilizing compound having a hydrophobic-lipophilic balance (HLB) of at least 8 and whose lipophilic portion comprises at least one ethylenic unsaturation. The aqueous dispersion is useful as a film-forming component of coating compositions.
U.S. Pat. No. 4,451,596 describes water-dilutable alkyd and acrylate resins for use in water-dilutable lacquer systems. A method for the preparation of water-dilutable resin preparations based upon alkyd and acrylate resins is also described.
European Patent 0 555 903 describes a water-dispersible hybrid polymer of an unsaturated fatty acid-functionalized polyester. In addition, aqueous dispersions of such a hybrid polymer for use in aqueous coating compositions with a high solids content and films produced by using such coating compositions are described.
WO 95/02019 describes an emulsion of an air-drying resin dispersed in water and the preparation of such emulsions. Hybrid emulsions of an alkyd resin and an acrylate resin are also described.
U.S. Pat. No. 5,538,760 describes a general process for cleaning and providing a protective shine to a hard surface by use of an alkyd/acrylic latex. The alkyd/acrylic latex is prepared from an aqueous emulsion of an alkyd resin and at least one monoethylenically unsaturated monomer. Upon heating of the aqueous emulsion, an alkyd/acrylic latex is formed which can then be applied to a hard surface.
The acrylic polymers of previous hybrids are either non-reactive or possess reactive groups (e.g. hydroxyl groups) which react, as do similar groups present in the alkyd resin, at elevated temperatures with aminoplasts such as melamine formaldehyde resins and only at elevated temperatures.
Uralkyd resins have also been used in various coating compositions. U.S. Pat. Nos. 4,178,425 and 4,180,645 describe uralkyd containing coating compositions having high solids content. More specifically, U.S. Pat. Nos. 4,178,425 and 4,180,645 each describe autooxidizable coating compositions based on (1) a member of the group consisting of an organic polyisocyanate, an isocyanate-modified drying oil or a urethane oil, and a uralkyd; (2) at least one non-volatile reactive liquid monomer selected from the group consisting of dicyclopentenyloxyalkyl acrylate and dicyclopentenyloxyalkyl methacrylate; and (3) an effective amount of a polyvalent metal-containing complex or salt that catalyzes the curing of (1) and (2).
U.S. Pat. No. 4,222,911 describes a coating composition containing a polyester diol extended uralkyd resin. The polyester diol extended uralkyd resin is prepared by reacting an oil modified alkyd resin, a polyester diol having a number average molecular weight in the range of from about 800 to about 4000, and a diisocyanate.
U.S. Pat. No. 3,778,395 describes a printing ink containing a color body and an oxidation vehicle. The oxidation vehicle is based on a modified uralkyd consisting of the reaction product of an alkyd prepolymer and a polyisocyanate.
U.S. Pat. No. 5,422,392 describes an aqueous ambient dry paint coating based on an addition copolymer matrix polymer of a polyurethane or polyester oligomer and an ethylenic monomer. The coating is free of organic coalescing solvents.
RU 2017780 describes a protective coating composition containing a uralkyd resin modified with an N,N'-substituted aliphatic amine, a drying agent, a cyclohexanone oxime and an organic solvent. SU 924184 describes the use of water soluble mixtures based on phenol formaldehyde and alkyd, alkyd-epoxide or uralkyd resins in electrophoretically produced polymer coatings.
SU 537099 describes rapidly drying uralkyd resins. Such uralkyd resins are prepared by reacting a modified oligoester with an isocyanate in the presence of an aliphatic alcohol and a N,N'-disubstituted aliphatic amine. SU 537104 describes the use of a uralkyd resin as an undercoating in aerosol form. The uralkyd resin is based on the reaction product of toluene diisocyanate with an ethriphthalic oligoester modified with dehydrated castor oil.
Various coating compositions have been prepared from polymer emulsion dispersions. U.S. Pat. No. 4,011,388 describes a process for preparing an aqueous polymer emulsion by polymerizing an aqueous dispersion of at least one polymer (e.g. cellulosic compounds) and at least one monomer (e.g. acrylics, methacrylics, styrene) to form an emulsion of a substantially homogeneous blend of at least two polymers.
U.S. Pat. No. 5,686,518 describes an essentially stable monomer mini-emulsion which includes water, a surfactant, a monomer or mixture thereof, and at least one polymer which functions as a polymeric co-surfactant. The monomer mini-emulsion is characterized by small monomer droplet size. Such an mini-emulsion can be polymerized to a polymer latex.
U.S. Pat. No. 5,569,715 describes a process for forming a hydrophobically modified emulsion and a modified emulsion polymer. The emulsion polymer is formed by combining a hydrophobic polymeric compound and an .alpha.,.beta.-ethylenically unsaturated monomer to form a mixture and then subjecting the mixture to high shear to form surfactant stabilized particles of the hydrophobic polymer and monomers. The .alpha.,.beta.-ethylenically unsaturated groups of the particles can be co-polymerized to form a hydrophobically modified core polymer. Addition of at least one more monomer including at least one .alpha.,.beta.-ethylenically unsaturated hydrophilic monomer followed by emulsion polymerization results in the formation of a hydrophobically modified emulsion polymer.
Non-water reducible, i.e. solvent-borne, alkyds or uralkyds have not received much attention due to the difficulty in incorporating them into a waterborne system. Accordingly, there still exists a need in the art for a method of imparting water-reducibility to solvent-borne alkyds or uralkyds.